1. Field of the Invention
The present invention relates to a method of manufacturing a printed circuit board (referred to as PCB hereinafter), and more particularly to a method of manufacturing a PCB in which a viahole is formed by employing a so-called build-up technique for successively forming inner layer circuits and insulating layers.
2. Description of the Prior Art
According to the method disclosed in Japanese Laid-Open Patent Publ. No. 3-3298, after forming a first copper conductor pattern 1 on a board 2 (FIG. 1A), the surface 3 of the conductor pattern 1 is subjected to a roughening process (FIG. 1B) to increase the adhesive force between the conductor pattern 1 and a resin film 5 to be coated on the conductor pattern 1 as shown in FIG. 1C.
Then, the surface 6 of the resin insulating layer 5 is roughened to improve the bonding force with a plated layer 7 to be formed thereon and an exposed surface of the first conductor pattern 1 is made flat by a soft etching process as shown in FIG. 1D to improve an electrical connection with the second conductor pattern 7 which is formed by platings as shown in FIG. 1E such that a viahole 8 is formed on the exposed flat surface of the first conductor pattern 1.
In the roughening process for the first copper conductor pattern 1, black needle crystals of copper oxide are grown chemically to enlarge the surface area of the copper conductor pattern and improve its bonding force by the anchor effect due to pores formed on the surface of the conductor pattern 1. But such a roughening process generates a so-called pink ring or halo caused by the dissolution of copper oxide into an acidic solution used in the plating process of the second conductor pattern 7. The formation of the pink ring at the periphery of the viahole causes peeling of the resin insulating layer at the periphery of the viahole due to corrosion of copper oxide present on the adhesion surface of the resin insulating layer and the conductor pattern 1. To prevent the undesired pink ring phenomenon, the prior art recommends to subject the roughened surface of the first copper layer to a reduction process prior to forming the resin insulating layer 5.
However, such a reduction process likewise reduces the above-mentioned anchor effect.
Moreover, since the roughening process for the resin insulating layer uses a powerful oxidizing agent, the first conductor pattern which was already treated by the reduction process tends to be oxidized again and thus the recommended reduction process cannot effectively prevent the pink ring phenomenon.